So, your workout has you doing 4 sets of 5 reps for this exercise, 3 sets of 8 after that, and—oh, thank goodness—only 2 sets of 50 to finish it out. Well, hey, the good news is that these rep numbers aren’t just based on a sadistic desire to see you huff and puff. Here’s how they differ and what they mean for you.

Recall that reps is simply the shorthand for the number of repetitions that you perform of a given exercise before you pause and rest (or pass out or whatever). Different weight training programs typically include a variety of rep schemes that all seem to have been drawn from a “do this much” hat. But take a closer look at several programs, and you’ll spot a few frequently used rep ranges:

1 to 5 reps: This range makes up the lower end of the reps that is associated with increasing strength.

6-12 reps: This is an intermediate to higher rep range that is generally associated with getting more or bigger muscles.

12-15+ reps: Anything higher than 12 helps with improving strength endurance (i.e. how long you can keep exerting a certain level of strength before your muscle fatigues), which contributes to helping you get bigger muscles, and consequently, stronger.

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While many experts stand behind these rep ranges as giving the described training outcome, the truth is that you can build muscle, get stronger, and lose weight within a variety of rep ranges—though, some rep ranges might be better than others.

Lower Reps Improve Strength

If you’re keen on Hulk-smashing it up, a lot of strength-focused programs will have you lifting extremely challenging weights for fewer reps.

The findings of one study published in the Journal of Strength & Conditioning support that heavier weights for lower reps are better for increasing maximal strength. Researchers took 38 subjects and divided them among four training groups: 3-5 reps; 13-15 reps; 23-25 reps; and a control with no training.

At the end of a 7-week period, researchers re-tested all of the groups and observed the greatest strength increases in the 3-5 rep range group. They outperformed all others, with noted significant improvements over those in the 23-25 reps group. (Interestingly, muscle growth was observed to be fairly consistent across all groups—more on that in a bit.)

This and other research are in line with the heavy, low-rep training of strength-focused athletes, such as Olympic lifters and powerlifters. For these guys and gals, strength is generally defined as their ability to (safely) lift the heaviest amount of weight possible for one rep—which, by the way, isn’t predictably based on the amount of Schwarzenegger-level muscle they have either. Rather, your ability to lift something is largely thanks to your central nervous system, which essentially helps your “muscle memory” become better and more efficient at a given movement.

Higher Reps Improve Strength Endurance

Conversely, training yourself to lift lighter weights at higher reps allows you to be better at lifting lighter weights for more reps. You’ve also probably been told that lifting lighter weights for a high number of reps will help you gain more muscle. That’s not exactly incorrect. It can, but there’s a bit more to poking and prodding your body to grow muscles than simply banging out a crazy number of reps.

According to this excellent paper published in the Journal of Strength & Conditioning, muscle growth is determined by a number of factors, the most important of which include muscle damage, metabolic stress, and mechanical tension. To understand those terms in plain English, think of the soreness after a new or hard workout, the “burn” when you’re lifting or fatiguing your muscles, and the feeling that your arms are about to be ripped out of your shoulder sockets from trying a way-too-heavy deadlift, respectively.

There’s No Exact Rep Range For Bigger Muscles

Many stand by the 8-12 rep range as being “optimal” for muscle growth, but nothing is particularly magical about that range. Greg added that no single rep range can optimize all of the factors that help with muscle growth.

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Don’t just take my word for it: this paper, also in the Journal of Strength & Conditioning, examined the effects of low- and high-load resistance training among trained individuals, and basically indicated that you’d still potentially gain about the same amount of muscle regardless of whether you’re doing 25 reps or 8 reps.

There’s even an interesting study in Experimental Gerontology on high- and low-rep training with elderly adults that showed consistent muscle growth across all groups, including one that performed up to 100 reps. A hundred reps obviously is extreme (not to mention, inefficient and boring-as-hell in the real world), but the study does dramatically underscore the point that any rep range works for muscle growth, as long as you are putting in really hard effort and taking your sets to failure.

Whatever your goal, effort is key. In fact, it’s more important than the number of reps itself regardless of your fitness goal. In other words: if you want to lose weight, work hard; if you want to get bigger or more muscles, work hard.

Basically, the exact same process happens to your muscles when you take a set to failure no matter what rep range you’re using. Your muscles grow the same because of what’s happening at the muscular level, but your nervous system is also learning the rep ranges that you practice. This is why performance increases the most in the specific rep ranges in which you lift, whether that’s very low reps (maximal strength) or fairly high reps (strength endurance). So, for people [with specific goals], the best thing to do would be to just pick a rep range, put in lots of effort per set for multiple sets, and then eat in a way that will make their body composition the way they want it.

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So, think of your workouts in terms of “effort per set” rather than strictly just sets and reps, according to Nathan. Moreover, the best way to gauge hard effort is how close you are getting to “not being able to complete another rep.”

How to Get the Best of Both Worlds

Many strength coaches, including Greg, put their athletes on programs that combine both high-rep and low-rep ranges, but structure them in a way that lets them reap the benefits of both muscle growth and greater improvements in strength. This type of program design is called periodization, with which you vary intensity, training specificity, and volume (overall work done). Picture a wavelength, with these factors going up and down and changing within a certain time period.

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Moreover, there are different types of periodization, and often they’re dependent on what the trainee aims to do—whether he is: gearing up for competition, conditioning in the off-season, hitting a specific goal, and so on. But for regular ol’ gym-enthusiasts like us, Greg says:

The way you vary your training is up to you. Classic linear periodization works very well, and involves working from lighter, higher rep training (generally starting around 60-65% of your one- rep max for sets of 12-15 reps) to heavier, lower rep training (generally ending around 90-95% of your one-rep max for sets of 1-3 reps) over the course of 8-16 weeks.

Other forms of periodization involve working through a variety of rep ranges for a single lift or muscle group in a single week, like this:

Day 1: sets of 10-12 reps

Day 2: sets of 6-8 reps

Day 3: sets of 2-4 reps

Or you can cycle through the rep ranges on a weekly basis, which can look something like:

Week 1: sets of 10-12 reps

Week 2: sets of 6-8 reps

Week 3: sets of 2-4 reps

Week 4: sets of 10-12 reps (with slightly heavier weights)

All of these methods work better than just sticking with a single set and rep scheme for all of your training, and they’re all similarly effective.

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However you decide to change up your training, make sure you are generally increasing the amount of weight to your lifts over time (it doesn’t have to be every week) and working your butt off every workout.

The Bottom Line

Whether you’re training with low reps or high reps in your program, know that both ranges can be effective at promoting muscle growth and fat loss. However, you can (and should) include variations of both in a smart way to improve your training, and more importantly, to avoid being bored from doing the same exercises for the same number of reps and sets every week.

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Illustration by Nick Crisuolo.

Stephanie Lee is a nomadic writer with a Sriracha problem. Visit her blog at http://fitngeeky.tv/ for her lighter takes on fitness and her shenanigans. You can also follow her on Twitter and Facebook.